1. Field of the Invention
The present invention relates to a long ink jet print head in which a plurality of relatively short nozzle chips provided with nozzles are precisely arranged (what is called a joined head), an ink jet printing apparatus that prints images using this ink jet print head, an ink jet printing method, and a method and program for setting print conditions.
2. Description of the Related Art
The following printing apparatuses are configured to print images (including characters and symbols) on print media such as sheets, thin plastic plates, or the like: those which are used for printers, copiers, and the like or which are used as composite electronic equipment including a computer, a word processor, or the like as well as output equipment such as a workstation. These printing apparatuses can be classified into an ink jet type, a wire dot type, and a laser beam type according to a printing system.
Serial type printing apparatuses perform a printing operation while moving printing means (print head) in a main scanning direction crossing a direction in which a print medium is conveyed (sub-scanning direction). Every time the printing means finishes the printing operation for one main scan, the print medium is conveyed by a predetermined amount in the sub-scanning direction. Images are sequentially printed on the print medium by repeating the printing operation and a conveying operation of conveying the print medium as described above.
What is called a line type printing apparatus carries out printing while conveying the print medium in the sub-scanning direction without moving the printing means in the main scanning direction.
Ink jet printing apparatuses carries out printing by allowing an ink jet print head serving as printing means to eject ink to the print medium. Such an ink jet printing apparatus has the advantages of facilitating a reduction in the size of the ink jet print head, enabling high-definition images to be printed at high speed, enabling what is called ordinary paper to be printed without any special treatment to reduce running costs, reducing noise by using a non impact system, and facilitating the use of arrangements for forming color images using multicolor inks. In particular, an ink jet printing apparatus using what is called a full-multi type ink jet print head enables a further increase in the speed of image formation; the full-multi type ink jet printing apparatus has a large number of nozzles (ink ejection openings) arranged in a direction orthogonal to the print medium conveying direction. Much attention is being paid to this type of ink jet printing apparatus because it is expected to be used for on-demand printing, the need of which has recently been growing.
In contrast to printing of newspapers or magazines, which involves several million copies per printing process, the on-demand printing need not achieve a print speed corresponding to hundred thousand copies per hour. However, it has been desired to reduce labor required for the on-demand printing. The line type ink jet printing apparatus using the full-multi type print head achieves a lower print speed than conventional offset printing apparatuses. However, this type of ink jet printing apparatus eliminates the need to produce printing plates to enable a reduction in required labor and is thus optimum for the on-demand printing.
The line type ink jet printing apparatus using the full-multi type print head needs to provide a resolution of 600×600 dpi (dots/inch) in order to print monochromatic images such as texts. It needs to provide a high resolution of at least 1,200×1,200 dpi in order to print full color images such as photographs. It also needs to achieve a print speed corresponding to 30 pages per minute for A3-sized print media.
On the other hand, images taken with a digital camera or the like may be printed on L-sized print media as is the case with the prior art or on small print media such as postcards. Thus, images are very often printed on print media of different sizes.
However, for the full-multi type ink jet print head, it is difficult to machine, without any defects, all of a large number of ejection openings arranged across the width of a print area on the print medium and all elements (ink jet print elements) required to eject ink from the ejection openings. For example, a full-multi type print head used to print photographic images on large-sized sheets in, for example, offices requires about 14,000 ejection openings (print width: about 280 mm) in order to print images on A3-sized sheets at a resolution of 1,200 dpi. It is difficult to machine, without any defects, all ink jet print elements corresponding to the large number of ejection openings. Given that such print heads free from any defects can be manufactured, their efficiency percentage is very low and their manufacture costs are enormous.
Thus, a configuration using what is called a joined head has been proposed for the line type ink jet printing apparatus. The joined head is a long print head formed by precisely arranging a plurality of relatively inexpensive, short chips for print heads used for the serial type ink jet printing apparatus. However, with the joined head, image density is disadvantageously likely to be uneven in printed images corresponding to the joining portions among the plurality of chips. Specifically, if misalignment occurs between the arrays of nozzles (ejection openings) in the adjacent chips, the nozzle pitch in the joining portion between the chips is different from that in the other parts. This may result in a stripe-like high- or low-density portion (joining stripe) on a printed image.
Several improvements have been proposed to prevent generation of joining stripes due to the joined head.
For example, the following have been proposed: a method of precisely arranging the joining portions among the chips and a method of using an arranging device to reduce a variation in nozzle pitch (Japanese Patent Application Laid-Open No. 2003-305853), that is, a method of improving the physical machining precision of the print head. A method has also been proposed which, rather than simply arranging the adjacent chips so that nozzles located at the ends of the respective nozzle lines are adjacent to each other in the direction of the nozzle lines, arranges the adjacent chips so that two sets of a plurality of nozzles located close to the ends of the respective nozzle lines overlap each other (Japanese Patent Application Laid-Open No. 05-057965). During a printing operation, the overlapping nozzles eject ink so as to make possible joining stripes unnoticeable. A method has also been proposed which varies the amount of ink ejected from nozzles located in the joining portion between the chips so as to make possible joining stripes unnoticeable.
However, even with the above measures for suppressing the occurrence of joining stripes, if the array of a plurality of chips becomes defective during a process of manufacturing print heads, suppressing the occurrence of joining strips is difficult. Thus, if long print heads are manufactured by arranging a large number of chips, even when a defect occurs in only one of the joining portions among the chips, that print head as a whole must be rejected. This reduces the yield of print heads. Moreover, the improved precision of a device for arranging a plurality of chips increases manufacture costs. If image processing is executed to control printing depending on the misalignment in the joining portion between the chips, separate means are required for determining the amount of misalignment on the basis of a printed test pattern.